I’ve had 4 slots (including the starting one) before i started upgrading, went to the gem store and bought a Bank Tab Expansion from there (I didn’t use the direct way from the bank), the transaction was successful, and it appeared in my “recent purchases” bar, but I didn’t get either the item to pickup or the expansion directly… I’ve reported the bug in game, but wanted to post it here so I’ll be sure i get the answer. I managed to purchase 3 tabs directly on the bank unlock bar, with no problems, but that one i purchased on the store is still missing, so now i have 7 tabs instead of 8.

